This invention relates to aluminum alloys, and more particularly to aluminum casting alloys, especially those used for pressure-die casting.
The total weight of die cast aluminum products exceeds the total weight of aluminum alloy castings prepared by all other casting techniques combined. Further, aluminum alloys are used more frequently in die castings than any other base metal. The extensive use of aluminum die-cast alloys for various articles such as machine parts, housings for machines, electronics, instruments, etc. is attributable at least in part to the high dimensional accuracy and smooth and attractive casting surfaces of aluminum die-cast alloys in the as-cast condition.
While many of the known aluminum castings alloys exhibit acceptable corrosion resistance for moderately harsh environments, the known aluminum casting alloys, and in particular the known aluminum die casting alloys, are not sufficiently resistant to corrosion for certain highly corrosive environments. For example, aluminum castings that are used in highly corrosive exterior automotive applications in which the castings are routinely exposed to temperature extremes, water, snow, ice and humidity, as well as corrosion inducing materials such as salt, and dirt and road grime that can retain moisture and salt, eventually tend to exhibit significant corrosion. The known aluminum die casting alloys generally contain silicon in an amount that is effective to improve fluidity of the alloy in a molten state during the die casting operation. Additions of silicon also improve hot tear resistance and have beneficial effect on tensile strength and elongation properties of cast compounds. The most commonly used aluminum-silicon alloy for die casting is alloy 380.0 and its modifications. The 380.0 family of alloys exhibit a balanced combination of low cost, strength, and corrosion resistance, as well as high fluidity and freedom from hot shortness that are required to achieve good die-castability. However, the 380.0 alloys and other aluminum die casting alloys typically contain copper in an amount of from about 2 to about 4.5 percent. Copper is added to improve strength and hardness, but generally reduces resistance to general corrosion. Thus, the 380.0 family of aluminum alloys does not exhibit high corrosion resistance, and is unsuitable for certain automotive applications, such as for exposed parts that are mounted in the engine compartment of a vehicle.
Where better corrosion resistant is required, alloys low in copper, such as 360.0 and 413.0 are typically used. These alloys still contain a significant amount of copper (0.6 and 1.0 percent by weight, respectively) and consequently show clearly visible signs of corrosion when exposed to a highly corrosive environment for a prolonged period. Thus, the known aluminum die casting alloys are not especially well suited for those applications in which it is desired to use a die cast aluminum component which maintains a good, non-corroded appearance after prolonged exposure to a highly corrosive environment.
Attempts to further improve corrosion resistance by lowering the copper content below 0.6 percent would be expected to result in unsatisfactory strength properties for most applications. Therefore, it would be highly desirable to have an aluminum die casting alloy that is highly resistant to corrosion yet exhibits adequate strength for use in making automotive components that are mounted in the engine compartment of a vehicle, and components for outdoor use such as light fixtures, electronic housings, telephone cases, etc.
This invention is directed to an aluminum alloy having improved corrosion resistance and excellent strength characteristics. The aluminum alloys of this invention are characterized by a very low copper content, a manganese content that is sufficient to input excellent strength properties, and a silicon content that is sufficient to impart excellent fluidity, hot tear resistance and feeding characteristics for good die-castability.
These and other features, advantages and objects of the present invention will be further understood and appreciated by those skilled in the art by reference to the following specification and claims.